1. Field
The present disclosure relates to a vehicle drive system, and more particularly relates to a vehicle drive system that switches the drive state of a vehicle when slipping is occurring and after slipping has occurred.
2. Description of the Related Art
There has been conventionally proposed a technology where, when front wheels or rear wheels of a vehicle slip, a two-wheel drive state (hereinafter referred to as “2WD”) is switched to a four-wheel drive state (hereinafter referred to as “AWD”), and AWD is continued while a preset four-wheel drive continuing time elapses from the point that the slipping state has been resolved (e.g., see Japanese Unexamined Patent Application Publication No. 2008-120119). This Japanese Unexamined Patent Application Publication No. 2008-120119 disclose technology where not only is AWD continued until the preset four-wheel drive continuing time elapse in this way, but also a corrected four-wheel drive continuing time is calculated where the value of the four-wheel drive continuing time is variable in accordance with the amount of slip (magnitude and degree of slipping), and AWD is continued until the calculated four-wheel drive corrected continuing time elapses.
However, even if the calculated slip amount is the same, road conditions will greatly vary from time to time. Accordingly, there is a possibility that the amount of time over which to continue AWD cannot be appropriately set in a system where the four-wheel drive continuing time is decided beforehand without taking road conditions into consideration, or a system where the four-wheel drive corrected continuing time is decided simply based on slip amount without taking road conditions into consideration.
Accordingly, there has been concern that vehicle stability might be at risk due to uniformly switching from AWD to 2WD based on four-wheel drive corrected continuing time or the like, regardless of a situation where the friction coefficient (μ) of the road surface is low and AWD should be continued. On the other hand, needlessly continuing AWD for extended periods of time based on four-wheel drive corrected continuing time or the like, regardless of a situation where the friction coefficient of the road surface is high and continuing AWD is needless, may result in poor fuel consumption or electricity consumption (hereinafter referred to as “drive efficiency”).
It has been found to be desirable to provide a vehicle drive system that can improve drive efficiency while securing vehicle stability, by switching between drive states of the vehicle at a more appropriate timing.